1. Field of the Invention
The present invention relates to a bumper beam for holding a bumper, disposed in a front or rear end part of a vehicle.
2. Description of the Related Art
A bumper is attached to a front or rear end part of a vehicle to absorb shock and to protect the body of the vehicle and the passengers in longitudinal collision with another object. Generally, a bumper is attached to a bumper beam attached to free ends of longitudinal frame members (a pair of side frame members) so as to extend laterally. It is desirable, in view of protecting the body, that the bumper and the bumper beam are comparatively strongly built so that the same may not be damaged by a slight collision and do not need to be changed frequently.
FIGS. 5A, 5B and 5C show a typical, conventional bumper beam. As shown in FIG. 5A, a left stay 12a and a right stay 12b are attached to, for example, the front ends of a pair of longitudinal frames 11a and 11b, respectively, and a bumper beam 20 is attached to the stays 12a and 12b so as to extend laterally. The bumper beam 20 has a bumper beam body 13 having a closed sectional shape and a channel-shaped reinforcing beam 14 extended in the bumper beam body 13.
In the bumper beam 20, joining parts of the bumper beam body 13 associated with the front ends of the longitudinal frames 11a and 11b (FIG. 5C) and a middle part of the same (FIG. 5B) are substantially the same in shape, and joining parts of the reinforcing beam 14 associated with the front ends of the longitudinal frames 11a and 11b (FIG. 5C) and a middle part of the same (FIG. 5B) are substantially the same in shape.
Since the structural strength of joining parts of the bumper beam 20 that are attached to the front ends of the longitudinal frames 11a and 11b is the same as that of a middle part of the bumper beam 20, the bumper beam body 13 and the reinforcing beam 14 of the bumper beam 20 have high strength to withstand a strong shock that applies a compressive force exceeding a predetermined level on the bumper beam 20, such as a shock that is exerted on the bumper beam 20 by a high-speed collision, let alone a shock that is exerted on the bumper beam 20 by a slight collision. Consequently, the shock of collision is transmitted directly to the longitudinal frames 11a and 11b at a high-speed collision, and the longitudinal frames 11a and 11b are squeezed to absorb the shock.
However, it is effective in protecting the passengers to let not only the frame of the body but also the bumper yield effectively to absorb the shock of collision by the bumper at high-speed collisions.
There have been proposed various bumpers having bumper beams meeting such directly opposed characteristics necessary for effectively absorbing shocks at slight collisions and strong collisions. However, all those known bumper beams are complicated in structure, need a shock absorbing mechanism having members capable of moving for a long longitudinal stroke, are costly and/or affect styling adversely.
Accordingly, it is an object of the present invention to solve the problems in the aforesaid conventional bumper beams and to provide an inexpensive, lightweight, highly safe bumper beam having an optimum mechanical characteristic and capable of effectively coping with slight and strong collisions.
According to one aspect of the present invention, a bumper beam to be attached to a front or rear end part of a vehicle comprises a bumper beam body attached to end parts of longitudinal frames so as to extend laterally; and a reinforcing beam extended in the bumper beam along the same; wherein parts of at least either the bumper beam body or the reinforcing beam, around joining parts attached to the longitudinal frames have a strength lower than that of other parts of the bumper beam body or the reinforcing beam so that the joining parts may be deformed by a compressive force exceeding a predetermined level.
In the bumper beam according to the present invention, it is preferable that the bumper beam body or the reinforcing beam includes a lateral upper wall, a lateral lower wall and a front wall formed integrally with the upper and the lower wall to receive a longitudinal shock exerted on the vehicle, and parts of at least either the upper wall or the lower wall around the joining parts are inclined parts inclined to the front wall.
In the bumper beam according to the present invention, it is preferable that the bumper beam body or the reinforcing beam includes a lateral upper wall, a lateral lower wall, a front wall formed integrally with the upper and the lower wall to receive a longitudinal shock exerted on the vehicle, and openings are formed in parts of at least either the upper wall or the lower wall around the joining parts, respectively. Preferably, the openings are holes formed in the upper or the lower wall, or recesses formed in an edge of the upper or the lower wall, not connected to the front wall.
In the bumper beam according to the present invention, it is preferable that the bumper beam body or the reinforcing beam includes a lateral upper wall, a lateral lower wall and a front wall formed integrally with the upper and the lower wall to receive a longitudinal shock exerted on the vehicle, and inclined parts inclined to the front wall and openings are formed in parts of at least either the upper wall or the lower wall around the joining parts, respectively. Preferably, the openings are holes formed in the upper or the lower wall, or recesses formed in an edge of the upper or the lower wall, not connected to the front wall.
In the bumper beam according to the present invention, it is preferable that the parts of the front wall of the reinforcing beam around the joining parts are spaced from the bumper beam body.
According to the present invention, the strength of the joining parts of the bumper beam (a bumper beam body or a reinforcing beam) attached to the end parts of the longitudinal frames is lower than that of other parts of the bumper beam so that the joining parts may be deformed by a compressive force exceeding a predetermined level. Therefore, the bumper beam (the bumper beam body or the reinforcing beam) has a strength sufficient to withstand a compressive force below the predetermined level that is exerted thereto by a slight collision, the bumper beam is not damaged by such a low compressive force and hence the bumper beam does not need to be changed frequently. When a compressive force exceeding the predetermined level is exerted on the bumper beam by a high-speed collision, the joining parts of the bumper beam (the bumper beam body or the reinforcing beam) attached to the end parts of the frames buckle and collapse in an early stage of a high-speed collision to limit a maximum impact load to a low level and to absorb collision energy efficiently so that reduced collision energy may be exerted on the frames of the body of the vehicle and a reduced shock may be exerted on the passengers.
According to the present invention, the strength of the joining parts of the bumper beam body or the reinforcing beam, attached to the end parts of the frames can be reduced by forming inclined parts inclined to the front wall in parts of at least the upper or the lower wall of the bumper beam (the bumper beam body or the reinforcing beam). In this case, the distribution of strength on the bumper beam body or the reinforcing beam can be adjusted only through the variation of the sectional shape and the bumper beam body or the reinforcing beam can be easily manufactured without requiring boring or cutting work.
According to the present invention, the strength of the joining parts of at least either the upper or the lower wall of the bumper beam body or the reinforcing beam can be reduced by forming openings therein. In this case, the bumper beam body or the reinforcing beam can be formed in a simple sectional shape and can be easily manufactured. Particularly, when the openings (holes) are formed in the upper or the lower wall, the bumper beam body or the reinforcing beam can be easily manufactured by bending a plate even though boring work is necessary. When the openings (recesses) are formed by cutting parts of an edge of the upper or the lower wall, not connected to the front wall, the bumper beam body or the reinforcing beam can be easily manufactured by bending a plate even though cutting work is necessary. The cutting work for forming the recesses is simpler than the boring work.
The spacing of the parts of the front wall of the reinforcing beam around the joining parts from the bumper beam body promotes the initial collapsing of the bumper beam body.
According to the present invention, in the bumper beam having the bumper beam body and the reinforcing beam, the shape of the bumper beam body can be simplified without requiring any change in the shape of the bumper beam body only by adjusting the distribution of strength on the reinforcing beam for collapsing mode adjustment.
According to another aspect of the present invention, a bumper beam disposed on a front or rear end part of a vehicle, having joining parts attached to end parts of longitudinal frames, and extend laterally; wherein the joining parts have a strength lower than that of other parts of the bumper beam so that the joining parts may be deformed by a compressive force exceeding a predetermined level.